Kyung Seung Oh

High Density Renal Medulla on Unenhanced CT : Significance and Relation with Hyd ration Status

Purpose : To assess the effect of hydration status on renal medullary attenuation and to evaluate theincidence of dense renal medulla, as seen on unenhanced CT. Material and Methods : We prospectively studiedunenhanced CT scans of 12 healthy volunteers. Obtained done after 10 hours and 15 hours of dehydration and afteroral intake of 2L of water. BUN/Cr, urine specific gravity, urine osmole and hematocrit were evaluated after 10hours of dehydration. CT images were reviewed for the presence of dense renal medulla and differential attenuationof dense renal and isodense medulla and cortex at the same level. The density changes of renal medulla afterhydration were evaluated. and CT findings were compared with the results of biochemical studies. In addition, weretrospectively reviewed the CT scans of 200 consecutive patients for evaluation of the incidence of dense renalmedulla. Results : In 8 of 12 volunteers, dense renal medulla was seen on CT scan after dehydration. Meanattenuation was 71.3 ±10.42HU after 10 hours of dehydration, 68.6 ±13.54HU after 15 hours, and 34.5 ±11.47HUafter hydration. No significant attenuation differences were detected between 10 hours and 15 hours ofdehydration, but significantly lower attenuation values were noted after hydration. For isodense medulla, the meanattenuation value was 35.7 ±7.9HU after 10 hours of dehydration, 39.58 ±9.66HU after 15 hours, and 36.58±7.77HU after hydration. The mean attenuation values of cortex were 35.9 ±5 . 9 5 H U after 10 hours ofdehydration, 37.58 ±5.95HU after 15 hours, and 37.08 ±9.75HU after hydration. With regard not only to durationof dehydration, but also ti hydration, no differences in attenuation values were noted for renal cortex orisodense renal medulla. However, higher density was noted in dense renal medulla than in isodense medulla orcortex for the same duration of dehydration. After hydration, complete resolution was seen at five of eight sitesand incomplete resolution at three of eight sites. There was no correlation between CT attenuation and laboratoryresults. Dense renal medulla was seen in 17 of 200 consecutive patients. Mean attenuation values were 64.06±8.38HU for dense renal medulla, 37.15 ±8 . 4 4 H U for isodense renal medulla and 35.36 ±8.13HU for cortex.Conclusion : For the same duration of dehydration, dense renal medulla showed a higher attenuation value thanisodense medulla or cortex, a finding which was completely or incompletely resolved after hydration. Inconsecutive patients, the incidence of dense renal medulla was 8.5% In conclusion, this in-cidence is aphysiological, variable, reflecting dehydration status.